Conventionally, electric vehicles (EV) or hybrid electric vehicles (HV) control electric power that is to be supplied from an inverter to a motor generator for driving the vehicle to cause an output torque from the motor generator to conform to a target torque determined based on, for example, an amount of depression of an accelerator pedal.
To control the inverter in this manner, it is necessary to detect the state of rotation of the motor generator, or, in other words, an angle of rotation of the motor generator (an angle of rotation of a rotor). Resolvers are widely used for the detection of an angle of rotation of the motor generator. The inverter is controlled in accordance with an output from a resolver, and in turn, the phase of an alternating current that is to be supplied to the motor generator is controlled.
The resolver detects, by means of a coil, a magnetic field that is generated in response to the rotation of the motor generator to detect the angle of rotation of the motor generator, or, in other words, the phase of rotation of the rotor. Therefore, a deviation in the position of the point of origin of the resolver occurring due to, for example, an error in the position of attachment of the resolver results in inaccurate detection of the angle of rotation of the motor generator, and disables appropriate control of electric current that is to be supplied to the motor generator.
JP 2004-129359 A discloses correcting an error in the point of origin of a resolver based on an output from the resolver while a motor generator is being rotated. Performing such learning to correct an error in the point of origin of a resolver can eliminate problems in actual operation.
The learning-based correction of an error in the point of origin of a resolver is often performed in a factory before shipment, but may also be performed later during repair or inspection at a dealer. Further, it can also be performed as desired during actual driving.
During or before such learning, or, in other words, when learning has yet to be completed, the position of the point of origin of the resolver is inaccurate. As a result, the output from the resolver is incorrect, and, when the motor generator is controlled, the output torque from the motor generator becomes too high or too low. In particular, when the motor generator is controlled in rectangular wave control mode, a deviation in the point of origin of the resolver causes a significant influence.